/*
 * Copyright 2002-2006 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io;

import java.io.IOException;
import java.io.InputStream;

/**
 * {@link Resource}对于指定InputStream的实现类。仅当没有具体的资源实现类适用时使用。尽可能使用
 * {@link ByteArrayResource} 或者其他基于文件的实现类。<br/>
 * {@link Resource} implementation for a given InputStream. Should only be used
 * if no specific Resource implementation is applicable. In particular, prefer
 * {@link ByteArrayResource} or any of the file-based Resource implementations
 * where possible.
 * 
 * <p>
 * In contrast to other Resource implementations, this is a descriptor for an
 * <i>already opened</i> resource - therefore returning "true" from
 * <code>isOpen()</code>. Do not use it if you need to keep the resource
 * descriptor somewhere, or if you need to read a stream multiple times.
 * 
 * @author Juergen Hoeller
 * @since 28.12.2003
 * @see ByteArrayResource
 * @see ClassPathResource
 * @see FileSystemResource
 * @see UrlResource
 */
public class InputStreamResource extends AbstractResource {

	private final InputStream inputStream;

	private final String description;

	private boolean read = false;

	/**
	 * Create a new InputStreamResource.
	 * 
	 * @param inputStream
	 *            the InputStream to use
	 */
	public InputStreamResource(InputStream inputStream) {
		this(inputStream, "resource loaded through InputStream");
	}

	/**
	 * Create a new InputStreamResource.
	 * 
	 * @param inputStream
	 *            the InputStream to use
	 * @param description
	 *            where the InputStream comes from
	 */
	public InputStreamResource(InputStream inputStream, String description) {
		if (inputStream == null) {
			throw new IllegalArgumentException("InputStream must not be null");
		}
		this.inputStream = inputStream;
		this.description = (description != null ? description : "");
	}

	/**
	 * This implementation always returns <code>true</code>.
	 */
	public boolean exists() {
		return true;
	}

	/**
	 * This implementation always returns <code>true</code>.
	 */
	public boolean isOpen() {
		return true;
	}

	/**
	 * This implementation throws IllegalStateException if attempting to read
	 * the underlying stream multiple times.
	 */
	public InputStream getInputStream() throws IOException,
			IllegalStateException {
		if (this.read) {
			throw new IllegalStateException(
					"InputStream has already been read - "
							+ "do not use InputStreamResource if a stream needs to be read multiple times");
		}
		this.read = true;
		return this.inputStream;
	}

	/**
	 * This implementation returns the passed-in description, if any.
	 */
	public String getDescription() {
		return this.description;
	}

	/**
	 * This implementation compares the underlying InputStream.
	 */
	public boolean equals(Object obj) {
		return (obj == this || (obj instanceof InputStreamResource && ((InputStreamResource) obj).inputStream
				.equals(this.inputStream)));
	}

	/**
	 * This implementation returns the hash code of the underlying InputStream.
	 */
	public int hashCode() {
		return this.inputStream.hashCode();
	}

}
